﻿using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using ProjectEuler.Linq;

namespace ProjectEuler.Problems
{
    [EulerProblem(11, 70600674)]
    [Description("What is the greatest product of four numbers on the same straight line in the 20 by 20 grid?")]
    internal sealed class Problem011 : EulerProblem
    {
        public override Object Solve()
        {
            return Grid.Max(x => x.Product());
        }

        private sealed class NumberGrid : IEnumerable<Int32[]>
        {
            private readonly Int32 _length;
            private readonly Int32[,] _grid;

            public NumberGrid(Int32 length, Int32[,] grid)
            {
                _length = length;
                _grid = grid;
            }

            public IEnumerator<Int32[]> GetEnumerator()
            {
                for (var y = 0; y < Height; y++)
                {
                    for (var x = 0; x < Width; x++)
                    {
                        var series = new[]
                        {
                            GetAdjacentNumbers(x, y, 1, 0),
                            GetAdjacentNumbers(x, y, 0, 1),

                            GetAdjacentNumbers(x, y, 1, -1),
                            GetAdjacentNumbers(x, y, 1, 1),
                        };

                        foreach (var s in series.Where(s => s != null))
                        {
                            yield return s;
                        }
                    }
                }
            }

            public Int32 Width
            {
                get { return _grid.GetLength(1); }
            }

            public Int32 Height
            {
                get { return _grid.GetLength(0); }
            }

            private Int32[] GetAdjacentNumbers(Int32 x, Int32 y, Int32 dx, Int32 dy)
            {
                var result = new Int32[_length];

                for (int i = 0; i < _length; i++)
                {
                    result[i] = _grid[x, y];

                    x += dx;
                    y += dy;

                    if ((x < 0) || (x >= Width))
                    {
                        return null;
                    }

                    if ((y < 0) || (y >= Height))
                    {
                        return null;
                    }
                }

                return result;
            }

            IEnumerator IEnumerable.GetEnumerator()
            {
                return GetEnumerator();
            }
        }

        private static readonly NumberGrid Grid = new NumberGrid(4, new Int32[,]
        {
            {08,02,22,97,38,15,00,40,00,75,04,05,07,78,52,12,50,77,91,08},
            {49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,04,56,62,00},
            {81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,03,49,13,36,65},
            {52,70,95,23,04,60,11,42,69,24,68,56,01,32,56,71,37,02,36,91},
            {22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80},
            {24,47,32,60,99,03,45,02,44,75,33,53,78,36,84,20,35,17,12,50},
            {32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70},
            {67,26,20,68,02,62,12,20,95,63,94,39,63,08,40,91,66,49,94,21},
            {24,55,58,05,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72},
            {21,36,23,09,75,00,76,44,20,45,35,14,00,61,33,97,34,31,33,95},
            {78,17,53,28,22,75,31,67,15,94,03,80,04,62,16,14,09,53,56,92},
            {16,39,05,42,96,35,31,47,55,58,88,24,00,17,54,24,36,29,85,57},
            {86,56,00,48,35,71,89,07,05,44,44,37,44,60,21,58,51,54,17,58},
            {19,80,81,68,05,94,47,69,28,73,92,13,86,52,17,77,04,89,55,40},
            {04,52,08,83,97,35,99,16,07,97,57,32,16,26,26,79,33,27,98,66},
            {88,36,68,87,57,62,20,72,03,46,33,67,46,55,12,32,63,93,53,69},
            {04,42,16,73,38,25,39,11,24,94,72,18,08,46,29,32,40,62,76,36},
            {20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,04,36,16},
            {20,73,35,29,78,31,90,01,74,31,49,71,48,86,81,16,23,57,05,54},
            {01,70,54,71,83,51,54,69,16,92,33,48,61,43,52,01,89,19,67,48},
        });
    }
}
